Headlight tester

ABSTRACT

A device for use in determining the location of an edge of a pattern of a light source while either testing the alignment or aiming the low beam of a light source such as a No. 2 headlight, characterized by a pair of vertically spaced photoelectric devices which are located on a support such as a screen or board with one device above and one device below a predetermined desired position for the upper edge of the high intensity zone of a pattern of the light source and a second pair of photoelectric devices disposed on a separate support or the same board or screen on opposite sides of a predetermined desired position for the left edge of the high intensity zone of the pattern. Each pair of photoelectric devices is connected to a meter means such as a milliammeter which is capable of indicating a difference in the output of the two photoelectric devices of each pair. By relatively moving the pattern and the pairs of photoelectric devices either by aiming the headlight or by moving the support for the pairs of photoelectric devices to produce the greatest indication on the milliammeter, the edge, either the upper edge or the left edge of the high intensity zone, is aimed to coincide with the predetermined desired position.

United States Patent 1.

Schick July 17, 1973 HEADLIGHT TESTER [57] ABSTRACT 75 lnvemor;Frederick Schick Springfield L A device for use in determining thelocation of an edge of a pattern of a light source while either testingthe alignment or aiming the low beam of a light source such [73}Asslgnee' Dura corporatlon Springfield as a No. 2 headlight,characterized by a pair of verti- [22] Fil d; O 6, 1970 cally spacedphotoelectric devices which are located on a support such as a screen orboard with one device [21 1 Appl. No.: 78,367 above and one device belowa predetermined desired position for the upper edge of the highintensity zone of a pattern of the light source and a second pair of[52] US. Cl. r. 356/121 hotoelectric devices disposed on a separatesupport or {Sl Int. Cl. G01] 1/00 the game board or screen on oppositesides of a predel i Field Of Search 5 termined desired position for theleft edge of the high 250/219 DR intensity zone of the pattern. Eachpair of photoelectric devices is connected to a meter means such as amilli- [56] References Cited ammeter which is capable of indicatinga'difference in UNITED STATES PATENTS the output of the twophotoelectric devices oteach pair. By relatively moving the pattern andthe pairs of 2,643,l l7 6/1953 Frisbie et al. 350/2l9 WD photoelectricdevices either by aiming the headlight or yi i g g by moving the supportfor the pairs of photoelectric de- 310771139 2/1963 rzdh et al. .11:.11: 356/121 vices produce the greatest indium the mmiam PrimaryExaminer-R0nald L. Wibert Assistant Examiner-Conrad Clark At!0rney-Hill,Sherman, Meroni, Gross & Simpson meter, the edge, either the upper edgeor the left edge of the high intensity zone, is aimed to coincide withthe predetermined desired position.

4 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of thelnvention The present invention is directed to an aiming or testingdevice and particularly to the photoelectric means used therewith.

2. Prior Art Proper alignment of a headlight or headlights on anautomobile is required by various local, State and Federal requirementsand correct alignment is concerned with the upper horizontal and leftvertical edges of the high intensity zone of the headlight beam pattern.One lighting inspection code requires alignment of the low beam lightpattemsuch as that of a number 2 type headlight so the upper horizontaledge of the high intensity zone of the headlight is at the height of thehorizontal centerline of the headlight whenthe pattern is projected on ascreen at a distance of 25 feet. The code also requires that the leftedge of the high intensity zone of the pattern be displacedapproximately 2 inches to the right of the vertical centerline of theheadlight to minimize glare to oncoming drivers during nighttime drivingconditions.

Many types of devicesand methods for properly aiming headlights andtesting headlight alignment have been proposed. One method utilizesmechanical devices mounted on the built in aiming pads around the edgeof the face of the headlight lens to position the plane of the aimingpads in correct relationship with the horizontal and vertical axes ofthe headlamp. However, due to manufacturing tolerances such as irregularbeam patterns and variations in alignment of the plane of the aimingpads with the beam pattern edges, considerable variations in heart! aimcan result.

A second method for either aiming headlights or testing headlightalignment utilizes a screen having reference marks or lines and theoperator visually locates the edges of the high intensity zone of thelight beam with respect to the predetermined reference lines. However,such a method requires a darkened work area and is subject to operatorerrorsdue to judgment variations between operators as to the position ofthe edge of the high intensityzone.

A third method utilizes a device having photoelectric sensitive cellsarranged in a pattern to indicate the center of the high intensity zoneof the lamp. In such a device, the aiming of the center of the highintensity zone is believed to properly aim the left-hand vertical edgeand the upper horizontal edge. However, due to variations in the sizeand shape of the zone, such devices do not necessarily provideconsistent aiming of the lefthand vertical edge and the upper horizontaledge. This method can use an apparatus which is positioned adjacent tothe headlight and examples of the type of apparatus are illustrated inU.S. Pat. No.2,29l,l l4, Pat. No. 2,308,095 and U.S. Pat. No. 2,714,327.This method has also been used with an aiming screen such as disclosedin US. Pat. No. 3,077,139.

A fourth method for aligning the left-hand vertical edge and the upperhorizontal edge of high intensity zone of a headlight beam utilizes aprojection board and an arrangement of photoelectric cells such asdisclosed in U.S. Pat. Nos. 3,386,333 and 3,467,473. In both of thesepatents three cells are aligned on a vertical line and three cells areplaced on a horizontal line in a particular arrangement with regard tothe desired reference lines for both the upper horizontal edge and theleft-hand edge of the high intensity zone. In the device disclosed inU.S. Pat. No. 3,386,333, the. output of each of the three cells isconnected to a computer amplifier which obtains a factor or quantity bydividing the output of the cell disposed furthest in the high intensityzone by the difference of the intermediate cell minus the output of thecell disposed on the reference line.

When the edge is properly aimed, the quantity or factor has a minimumvalue. In the device disclosed in U.S. Pat. No. 3,467,473, the outputsof the three cells are placed in a computer amplifier which takes thesecond differential of the output to give an indication which has itsmaximum value when the edge is properly aimed. Both of these systems areexpensive to produce due to the electronic equipment necessary toutilize the outputs of the photo cells in the required mathematicalformulas.

SUMMARY OF THE INVENTION The present invention comprises an arrangementof photoelectric cells for determining the location of an edge of a beampattern from a light source and is utilized while either testing thealignment of a light source such as a headlight or aiming an edge of abeam pattern from the light source. The photoelectric cells are arrangedon a support means such as'a screen or board as a spaced pair with adesired reference line or desired position for the edge extendingtherebetween and a pair of photoelectric cells is connected to a metermeans, such as a milliammeter, which is connected in a manner todetermine the difference in the output of the two photoelectric cellswhich difference is at a maximum when the edge of the high intensityzonecoin cides with the predetermined reference line or desired position.

Accordingly, it is an object of the present invention to provide a lamptesting and aiming device capable of determining the location of an edgeof the high intensity zone of a headlight-and aiming it at the properposition.

Another object of the presentinvention is to provide a device forheadlight aimingand testing which determines the location of theedges ofa headlight high intensity zone regardless of variations in thestructure of the headlight.

A still further object of the present invention is a device for locatingthe edges of a highintensity zone of a headlight regardless of theoperator's skill.

Yet another object of the present invention is to provide a device forlocating the edges of the high intensity zoneof a light source whichdevice is relatively inex pensive to manufacture.

Other objects, features and advantages of the invention will be readilyapparent from the following description of a preferred embodimentthereof although variations and modifications may be effected withoutdeparting from the spirit and scope of the novel concept of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the aimingboard of the present invention;

FIG; 2 is a circuit diagram for the present invention;

FIG. 3, is a diagrammatic view showing the invention as used with acondensing lens and a smaller board or screen; and

FIG. 4 is a plan view of the board or screen of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principles of the presentinvention are particularly useful in a headlight aiming and testingsystem for an automotive vehicle headlight which includes an aimingboard or screen generally indicated at in FIG. 1. The board 10 has ahorizontal line 1 1 which is a predetermined reference line for an upperhorizontal edge 12 of the high intensity zone 13 of the light beampattern. A second reference line 14 is a vertical line placed on theboard at the predetermined position for the left vertical edge 15 of thehigh intensity zone 13.

One method of using this system would be to have photoelectric cellssupported by the board 10 in which the headlight of the vehicle islocated 25 feet in front of the board 10 with the horizontal centerlineof the headlight coinciding with the horizontal reference line 1 l andwith its vertical centerline located at a predetermined distance to theleft of the reference line 14. As mentioned above, in one recommendedprocedure for testing or aiming, the vertical centerline of theheadlight should be 2 inches to the left of the reference line 14.According to this recommended procedure, a tolerance of plus or minus 2inches is allowed on the location of the upper horizontal edge 12 withrespect to the reference line 11 and a tolerance of 2 inches to the leftand 4 inches to the right is allowable in the position of the edge 15with respect to the reference line 14.

To determine the position of the horizontal upper edge 12 and theleft-hand edge 15 of the high intensity zone 13, four light-sensitivemeans such as photoelectric cells or devices 17-20 are utilized. Thelight sensitive means are of a type that convert light energy intoelectromotive force or to state it in another manner create electricalenergy when exposed to light which amount of energy is proportional tothe intensity of light being projected on the cell.

The photoelectric devices 17 and 18 are arranged as a pair and arevertically spaced from each other on a line extending substantiallytransversely to the horizontal reference line 11. As illustrated, thedevice 17 is disposed below the line 1 l and the device 18 is positionedabove the line 11. The devices 19 and 20 are arranged on a horizontallyextending line which is transverse to the reference line 14 whichextends therebetween. As illustrated, the reference lines 11 and 14which pass between the pairs of photoelectric devices are at apredetermined distance from each of the photoelectric devices of theirrespective pairs.

To measure the output of each of the two pairs of photoelectric devices,a meter means such as a milliammeter 23 or 24 is provided. The meter'23is electrically connected to the photoelectric device 17 by leads 25 and26 and is connected to the photoelectric device 18 by leads 27 and 28.The meter 24 is connected to the photoelectric device 19 by leads 30 and31 and to the photoelectric device 20 by leads 32 and 33. Asillustrated, each of the meters 23 and 24 has an indicating needle andpreferably is a center null type meter.

As best illustrated in FIG. 2, a circuit diagram show ing the electricalconnection for the photoelectric devices 19 and 20 to the meter 24 isillustrated. The photoelectric device 19 has its negative terminalconnected to terminal of the milliammeter 24 by lines 41 and 42 and hasa positive terminal connected to the terminal 43 of the meter 24 bylines 45 and 46. The photoelectric device 20 has its negative terminalconnected to the terminal 43 of the meter 24 by lines 46 and 47 andterminal 40 of the meter 24 is connected by lines 42 and 48 to thepositive terminal of the device 20. Thus, if both photoelectric devices19 and 20 are creating an electromotive force, the current flow from thedevice 19 through the milliammeter 24 is opposite to the current flow ofthe photoelectric device 20.

With the photoelectric devices 19 and 20 arranged with respect to thereference line 14, the device 19 is located in the area of the highintensity zone 13 of the light beam and therefore is producingelectromotive force. On the other hand, the photoelectric device 20 isoutside of the zone 13 and is thus producing either none or a very smallamount of electrical current. When the edge 15 of the zone 13 is movedto the left, the amount of light projecting on the device 20 increasesso that its current output increases. Furthermore, the projecting oflight on the device 20 causes a reduction in the internal resistance ofthe device 20 which allows a portion of the current produced in thedevice 19 to flow through the device 20 and reduce the amount of currentflowing through the meter 24. Since the milliammeter 24 is indicatingthe relative difference between the two currents which are flowing inopposite directions through the meter, its reading will be changed asthe output of electromotive force from the device 20 increases. If theedge 15 of the zone 13 is moved to the right of the line 14, the amountof light being projected on the device 19 decreases causing a decreasein its electromotive force which causes a lowering of the current flowtherefrom.

To locate the edge 15 with respect to the line 14, the operator movesthe light beam horizontally to the left and then to the right anddetermines the maximum reading on the meter 24. At the maximum reading,the edge 15 will be aimed to coincide with the reference line 14. If theedge is moved to the left, the output from the device 20 is increasedand causes a drop in the reading of the meter. If the edge 15 is movedtothe right, the intensity of the light projected on the device 29decreases causing a decrease in the output to cause a reduction in themeter reading or indication.

The electrical circuitry for the devices 17 and 18 and the meter 23 isexactly the same as the previously described circuitry. Thus, the edge12 is aimed at the desired line 11 when the reading of the meter 23 isat a maximum. If the edge 12 is moved upward from the desired position,the photoelectric device 18 will increase its output which passesthrough the meter 23 in a direction opposite to the output of the device17 and will reduce the reading of the meter. If the edge 12 is movedbelow the line 11, the output of the device 17 decreases resulting in adecrease indication from the meter 23. Thus, to properly aim the edge 12at the line 11, the operator of the system moves the high intensity zone13 vertically up and down and determines the maximum meter reading andthen resets the adjustment screws on the headlight to obtain thatpredetermined maximum reading.

In another method of practicing the invention, the screen 10 is replacedby a small aiming board or screen 10a which is used in conjunction witha condensing lens C which reduces the size of the light pattern from alight source L (FIG. 3). The screen is a support means for photoelectricdevices 17a 20a (FIG. 4) which devices are arranged on the screen a in amanner similar to the arrangement of the photoelectric devices l7-20 inFIG. 1 with devices 17a and 18a on opposite sides of position orreference line 11a and connected to meter means 230 and the devices 19aand 20a on opposite sides of a reference or position line 14a andconnected to meter means 24a. The photoelectric devices may be mountedon the front surface of the screen or behind the screen and exposed tothe light beam through suitable apertures 51-54 therein (FIG. 4).Instead of using apertures, the screen may be translucent so that lightpassing therethrough impinges on the photoelectric devices.

Since the condensing lens C reduces the size of the pattern 13a, thescreen 100 is positioned relatively close to the light source L whichmay be a headlight or other light source such as a fog light or spotlight. The distance between the screen 10a and light source L isdetermined by the characteristic of the condensing lens C and isadjusted to have the effect of the 25 feet as previously explained.

In this form of the apparatus, the screen 10a is positioned in a zeroposition with respect to the light source by support structure notillustrated, so that a properly aimed headlight will have its leftvertical edge coincide with line 14a and upper horizontal edge coincidewith the line 1 la. To test the alignment of the headlight, the screen10a is moved to the right and left and then up and down by appropriatemeans in the support structure to obtain the maximum readings on meter24a and 230, respectively, which readings determine when the leftvertical edge and upper horizontal edge of the high intensity zone ofthe headlight being tested coincide with the predetermined position.lines 140 and 11a respectively. By measuring the amount and direction ofthe movement of the screen 10a from the zero position in both thevertical and horizontal direction on an appropriate scale which iscalibrated to show the corre' sponding distance of movement at 25 feetand which scale is provided on the support structure, the amount oferror in the alignment of the light source from a proper alignment canbe determined. If an error exists, the screen 10a is returned to thezero position and the headlight adjusted to properly aim the leftvertical edge and the upper horizontal edge at the position lines 14aand 1 la respectively. Thus the screen or board 10a can be used in adevice for either testing the alignment of a light source alone ortesting and correctly aiming the light source to be in the properalignment.

In the above-described embodiment, the board or screen 10a acts as asupport means for the two pairs of photoelectric devices 17a-20a whichsupport means is movable in a support structure. Instead of using ascreen or board 100 as a support means, each pair of photoelectricdevices can be mounted on a separate support means such as a bracketwith the desired position or reference line disposed between the devicesof each pair. Each of the brakets is movably mounted in the supportstructure by means such as calibrated knobs with one bracket beingmovable along a horizontal line and the other bracket being movablealong a vertical line. The means for moving the brackets have anappropriate scale which is calibrated toshow the corresponding distanceof movement at 25 feet and which scales provide the amounts of error ofthe alignment of both the horizontal edge and vertical edge of a lightsource from a proper aligned position. Thus, the arrangement of thebrackets with their pairs of photoelectric devices can be used eitherfor testing the alignment of a light source alone or for testing andcorrecting a light source to be in a proper alignment as describedhereinabove.

As mentioned hereinabove, an advantage of the present system over thoseof the prior art is its simplicity and inexpensive manufacturing costs.Another advantage is that although the pairs of photoelectric devicessuch as 17 and 18 should be of similar characteristics, manufacturingvariations therein will not effect the re sults during either testing oraiming of a headlight. Therefore, there is no necessity for calibratingthe photoelectric devices of each pair with respect to each other. Thusthe frequently required calibration of some prior art systems is notrequired by the photoelectric system of the present invention.

Although minor modifications and variations may be suggested by thoseversed in the art, it should be understood that I wish to embody withinthe scope warranted hereon all such modifications as reasonably andproperly come within the scope of my contribution to the art.

I claim as my invention:

1. In a system for determining a location of an edge of a high intensityzone of a light pattern of a light source such as a headlight of anautomobile, the improvement comprising:

a pair of light sensitive means for sensing the intensity of the lightprojected thereon;

means for supporting said pair of light sensitive means in a spacedapart relationship on a line extending transversely to the edge of thehigh intensity zone with a predetermined positionlocated therebetween sothat when the edge of the high intensity zone coincides with theposition, one of said pair is outside of the high intensity zone and theother of said pair is in said high intensity zone; meter means;

means connecting said pair of light sensitive means with one another andwith said meter means in a manner for indicating the difference in theintensity of the light sensed by each of said pair of light sensitivemeans so that the maximum indication of difference occurs when the edgeof high intensity zone coincides with said position;

each of said light sensitive means comprising a photoelectric devicehaving a negative terminal and a positive terminal;

the negative terminal of one of said devices being connected to thepositive terminal of the other of said devices; said connected negativeand positive terminals being connected to one terminal of said meterdevice; and

the remaining terminals of said devices being connected to anotherterminal of said meter device;

whereby electromotive force current from the device which will benormally located in said intensity zone when the edge thereof is on saidpredetermined position is opposite to the current flow of the devicewhich is normally outside of said intensity zone when said edge is onsaid position.

2. A headlight aiming device for use in a system to determine thelocation of an edge of a light source such as an edge of a highintensity zone of a light pattern of a headlight of an automotivevehicle, comprising:

a pair of light sensitive means for sensing the intensity of lightprojected thereon by converting light energy into electromotive forces;

means for supporting the pair of light sensitive means;

meter means for measuring the electromotive forces generated by the pairof light sensitive means;

said pair of light sensitive means being disposed on said supportingmeans on a line extending transversely to the edge of said light highintensity zone and having a predetermined position located therebetween;

said pair of light sensitive means being coupled to each other and saidmeter means being connected to each of said pair of light sensitivemeans in a manner to register the difference of the electromotive forcesproduced thereby so that relative movement of thesupporting means andthe edge of the high intensity zone to coincide with the predeterminedposition creates a maximum indication on the meter means;

each of said light sensitive means comprising a photoelectric devicehaving a negative terminal and a positive terminal;

the negative terminal of one of said devices being connected to thepositive terminal of the other of said devices;

said connected negative and positive terminals being connected to oneterminal of said meter means; and

the-remaining terminals of said devices being connected to anotherterminal of said meter means;

whereby electromotive force current from the device which will benormally located in said intensity zone when the edge thereof is on saidpredetermined position is opposite to the current flow of the devicewhich is normally outside of said intensity zone when said edge is onsaid position.

3. In a system for determining the location of both a horizontal and avertical edge of a high intensity zone of a light pattern of a lightsource such as a headlight of an automobile, comprising:

a pair of lightsensitive means for sensing the intensity of the lightprojected thereon;

means for supporting said pair of light sensitive means in a spacedapart relationship on a line extending transversely to the edge of thehigh intensity zone with a predetermined position located therebetweenso that when the edge of the high intensity zone coincides with theposition one of said pair is outside of the high intensity zone and theother of said pair is in said high intensity zone;

meter means;

means connecting said pair of light sensitive means with one another andwith said meter means in a manner for indicating the difference in theintensity of the light sensed by each of said pair of light sensitivemeans so that the maximum indication of difference occurs when the edgeof high intensity zone coincides with said position;

second means for determining the location of a second edge with respectto a second predetermined position;

said second means comprising a pair of light sensitive means for sensingthe intensity of the light projected thereon;

means for supporting said second pair of light sensitive means in aspaced apart relationship on a line extending substantially transverselyto the second edge of the pattern with said second predeterminedposition located between the second pair of light sensitive means;

second meter means;

means connecting said second pair of light sensitive means with oneanother and with said second meter means in a manner indicating thedifference in the intensity sensed by each of the second pair of lightsensitive means so that the maximum indication of difference by saidsecond meter means occurs when the second edge coincides with the secondposition;

the light sensitive means of both pairs converting light energy intoelectromotive force and wherein the indication of each of the metermeans is a difference of the magnitude of the electromotive forcecreated by the pair of light sensitive means connected thereto;

said light sensitive means of each pair comprising a photoelectricdevice having a respective negative terminal and a'respective positiveterminal; the negative terminal of one of said devices in each pairbeing electrically connected with the positive terminal of its pairmateand to one terminal of the meter means associated with that respectivepair;

the remaining terminals of each respective pair of photoelectric devicesbeing connected to another terminal of the associated meter means, eachof said meter means being a center null type meter; and j thearrangement being such that one of the devices of each pair is normallylocated within said high intensity light zone pattern when said edgesare in substantial coincidence with said predetermined positions and theremaining device of each pair is outside of said zone. 4. A headlightaiming device for use in a system to determine the location of an edgeof a light source such as an edge of a high intensity zone of a lightpattern of a headlight of an automotive vehicle, comprising:

a pair of light sensitive means for sensing the intensity of lightprojected thereon by converting light energy into electromotive forces;

means for supporting the pair of light sensitive means;

meter means for measuring the electromotive forces generated by the pairof light sensitive means;

said pair of light sensitive means being disposed on said supportingmeans on a line extending transversely to the edge of said light highintensity zone and having a predetermined position located therebetween;

said pair of light sensitive means being coupled to each other and saidmeter means being connected to each of said pair of light sensitivemeans in a manner to register the difference of the electromotive forcesproduced thereby so that relative movement of the supporting means andthe edge of the high intensity zone to coincide with the predeterminedposition creates a maximum indication on the meter means;

a second pair of light sensitive means for sensing the intensity oflight projected thereon by converting light energy to electromotiveforces;

a second means for supporting the second pair of light sensitive means;

a second meter associated with the second pair of light sensitive means;

said second pair of light sensitive means being mounted on the secondsupporting means on a line extending transversely to the first pair andbeing spaced apart with a second predetermined position locatedtherebetween;

said second pair of light sensitive means being coupled to each otherand said second meter means being connected to each of the lightsensitive means of the second pair in a manner to indicate thedifference in the electromotive forces generated therein so that therelative movement of the high intensity zone and the supporting means tohave an edge coinciding with each of said firstmentioned position and asecond position creates a maximum indication on each of said metermeans;

the light sensitive means of both pairs converting light energy intoelectromotive force and the indication of each of the meter means is adifference of the magnitude of the electromotive force created by thepair of light sensitive means connected thereto;

said light sensitive means of each pair comprising a photoelectricdevice having a respective negative terminal and a respective positiveterminal;

the negative terminal of one of said devices in each pair beingelectrically connected with the positive terminal of its pairmate and toone terminal of the meter means associated with that respective pair;and

the remaining terminals of each respective pair of photoelectric devicesbeing connected to another terminal of said meter means, each of saidmeter means being a center null type meter; and

the arrangement being such that one of the devices of each pair isnormally located within said high intensity light zone pattern when saidedges are in substantial coincidence with said predetermined positionsandthe remaining device of each pair is outside of said zone.

1. In a system for determining a location of an edge of a high intensityzone of a light pattern of a light source such as a headlight of anautomobile, the improvement comprising: a pair of light sensitive meansfor sensing the intensity of the light projected thereon; means forsupporting said pair of light sensitive means in a spaced apartrelationship on a line extending transversely to the edge of the highintensity zone with a predetermined position located therebetween sothat when the edge of the high intensity zone coincides with theposition, one of said pair is outside of the high intensity zone and theother of said pair is in said high intensity zone; meter means; meansconnecting said pair of light sensitive means with one another and withsaid meter means in a manner for indicating the difference in theintensity of the light sensed by each of said pair of light sensitivemeans so that the maximum indication of difference occurs when the edgeof high intensity zone coincides with said position; each of said lightsensitive means comprising a photoelectric device having a negativeterminal and a positive terminal; the negative terminal of one of saiddevices being connected to the positive terminal of the other of saiddevices; said connected negative and positive terminals being connectedto one terminal of said meter device; and the remaining terminals ofsaid devices being connected to another terminal of said meter device;whereby electromotive force current from the device which will benormally located in said intensity zone when the edge thereof is on saidpredetermined position is opposite to the current flow of the devicewhich is normally outside of said intensity zone when said edge is onsaid position.
 2. A headlight aiming device for use in a system todetermine the location of an edge of a light source such as an edge of ahigh intensity zone of a light pattern of a headlight of an automotivevehicle, comprising: a pair of light sensitive means for sensing theintensity of light projected thereon by converting light energy intoelectromotive forces; means for supporting the pair of light sensitivemeans; meter means for measuring the electromotive forces generated bythe pair of light sensitive means; said pair of light sensitive meansbeing disposed on said supporting means on a line extending transverselyto the edge of said light high intensity zone and having a predeterminedposition located therebetween; said pair of light sensitive means beingcoupled to each other and said meter means being connected to each ofsaid pair of light sensitive means in a manner to register thedifference of the electromotive forces produced thereby so that relativemovement of the supporting means and the edge of the high intensity zoneto coincide with the predetermined position creates a maximum indicationon the meter means; each of said light sensitive means comprising aphotoelectric device having a negative terminal and a positive terminal;the negative terminal of one of said devices being connected to thepositive terminal of the other of said devices; said connected negativeand positive terminals being connected to one terminal of said metermeans; and the remaining terminals of said devices being connected toanother terminal of said meter means; whereby electromotive forcecurrent from the device which will be normally located in said intensityzone when the edge thereof is on said predetermined position is opposiTeto the current flow of the device which is normally outside of saidintensity zone when said edge is on said position.
 3. In a system fordetermining the location of both a horizontal and a vertical edge of ahigh intensity zone of a light pattern of a light source such as aheadlight of an automobile, comprising: a pair of light sensitive meansfor sensing the intensity of the light projected thereon; means forsupporting said pair of light sensitive means in a spaced apartrelationship on a line extending transversely to the edge of the highintensity zone with a predetermined position located therebetween sothat when the edge of the high intensity zone coincides with theposition one of said pair is outside of the high intensity zone and theother of said pair is in said high intensity zone; meter means; meansconnecting said pair of light sensitive means with one another and withsaid meter means in a manner for indicating the difference in theintensity of the light sensed by each of said pair of light sensitivemeans so that the maximum indication of difference occurs when the edgeof high intensity zone coincides with said position; second means fordetermining the location of a second edge with respect to a secondpredetermined position; said second means comprising a pair of lightsensitive means for sensing the intensity of the light projectedthereon; means for supporting said second pair of light sensitive meansin a spaced apart relationship on a line extending substantiallytransversely to the second edge of the pattern with said secondpredetermined position located between the second pair of lightsensitive means; second meter means; means connecting said second pairof light sensitive means with one another and with said second metermeans in a manner indicating the difference in the intensity sensed byeach of the second pair of light sensitive means so that the maximumindication of difference by said second meter means occurs when thesecond edge coincides with the second position; the light sensitivemeans of both pairs converting light energy into electromotive force andwherein the indication of each of the meter means is a difference of themagnitude of the electromotive force created by the pair of lightsensitive means connected thereto; said light sensitive means of eachpair comprising a photoelectric device having a respective negativeterminal and a respective positive terminal; the negative terminal ofone of said devices in each pair being electrically connected with thepositive terminal of its pairmate and to one terminal of the meter meansassociated with that respective pair; the remaining terminals of eachrespective pair of photoelectric devices being connected to anotherterminal of the associated meter means, each of said meter means being acenter null type meter; and the arrangement being such that one of thedevices of each pair is normally located within said high intensitylight zone pattern when said edges are in substantial coincidence withsaid predetermined positions and the remaining device of each pair isoutside of said zone.
 4. A headlight aiming device for use in a systemto determine the location of an edge of a light source such as an edgeof a high intensity zone of a light pattern of a headlight of anautomotive vehicle, comprising: a pair of light sensitive means forsensing the intensity of light projected thereon by converting lightenergy into electromotive forces; means for supporting the pair of lightsensitive means; meter means for measuring the electromotive forcesgenerated by the pair of light sensitive means; said pair of lightsensitive means being disposed on said supporting means on a lineextending transversely to the edge of said light high intensity zone andhaving a predetermined position located therebetween; said pair of lightsensitive means being coupled to each other and said meter means beingconnEcted to each of said pair of light sensitive means in a manner toregister the difference of the electromotive forces produced thereby sothat relative movement of the supporting means and the edge of the highintensity zone to coincide with the predetermined position creates amaximum indication on the meter means; a second pair of light sensitivemeans for sensing the intensity of light projected thereon by convertinglight energy to electromotive forces; a second means for supporting thesecond pair of light sensitive means; a second meter associated with thesecond pair of light sensitive means; said second pair of lightsensitive means being mounted on the second supporting means on a lineextending transversely to the first pair and being spaced apart with asecond predetermined position located therebetween; said second pair oflight sensitive means being coupled to each other and said second metermeans being connected to each of the light sensitive means of the secondpair in a manner to indicate the difference in the electromotive forcesgenerated therein so that the relative movement of the high intensityzone and the supporting means to have an edge coinciding with each ofsaid first-mentioned position and a second position creates a maximumindication on each of said meter means; the light sensitive means ofboth pairs converting light energy into electromotive force and theindication of each of the meter means is a difference of the magnitudeof the electromotive force created by the pair of light sensitive meansconnected thereto; said light sensitive means of each pair comprising aphotoelectric device having a respective negative terminal and arespective positive terminal; the negative terminal of one of saiddevices in each pair being electrically connected with the positiveterminal of its pairmate and to one terminal of the meter meansassociated with that respective pair; and the remaining terminals ofeach respective pair of photoelectric devices being connected to anotherterminal of said meter means, each of said meter means being a centernull type meter; and the arrangement being such that one of the devicesof each pair is normally located within said high intensity light zonepattern when said edges are in substantial coincidence with saidpredetermined positions and the remaining device of each pair is outsideof said zone.